Microwave-induced synthesis of highly dispersed gold nanoparticles within the pore channels of mesoporous silica

Highly dispersed gold nanoparticles have been incorporated into the pore channels of SBA-15 mesoporous silica through a newly developed strategy assisted by microwave radiation (MR). The sizes of gold are effectively controlled attributed to the rapid and homogeneous nucleation, simultaneous propagation and termination of gold precursor by MR. Diol moieties with high dielectric and dielectric loss constants, and hence a high microwave activation, were firstly introduced to the pore channels of SBA-15 by a simple addition reaction between amino group and glycidiol and subsequently served as the reduction centers for gold nanoparticles. Extraction of the entrapped gold from the nanocomposite resulted in milligram quantities of gold nanoparticles with low dispersity. The successful assembly process of diol groups and formation of gold nanoparticles were monitored and tracked by solid-state NMR and UV-vis measurements. Characterization by small angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the incorporation of gold nanoparticles would not breakup the structural integrity and long-range periodicity of SBA-15. The gold nanoparticles had a narrow size distribution with diameters in the size range of 5-10 nm through TEM observation. The average particles size is 7.9 nm via calculation by the Scherrer formula and TEM measurements. Nitrogen adsorption and desorption isotherms gave further evidence that the employed method was efficient and gold nanoparticles were successfully incorporated into the pore channels of SBA-15.     

Base-catalyzed reactions enhanced by solid acids: Amine-catalyzed nitroaldol (Henry) reactions enhanced by silica gel or mesoporous silica SBA-15

The reactions of various aldehydes with CH₃NO₂ catalyzed by Et₃N, n-C₆H₁₃NH₂, and Me₂N(CH₂)₂NH₂ were accelerated by the addition of silica gel to give aromatic (aliphatic) β-nitroalcohols, aromatic nitroalkenes, and aromatic 1,3-dinitroalkanes, respectively. Mesoporous silica SBA-15 showed higher activity than silica gel for the synthesis of aromatic nitroalkenes by the reactions of the corresponding aldehydes with CH₃NO₂ catalyzed by n-C₆H₁₃NH₂.     

Synthesis of novel mesoporous silica spheres with starburst pore canal structure

Novel spherical mesoporous silica materials with uniform diameters and starburst mesopore structures were synthesized by a simple one-step procedure with ethanol as the co-solvent in dilute aqueous solution and their formation mechanism was proposed. The arrangement of the pore canal and the diameter of the sphere could be tailored by altering the concentration of ethanol.     

Temperature dependence of positron lifetime in ordered porous silica (SBA-3)

The temperature dependence of positron lifetime in uniform mesopores was analyzed. We used SBA-3 as the sample material, which possesses an ordered porous structure with uniform cylindrical mesopores. The positron lifetime corresponding to the annihilation in the mesopores increased gradually with a decrease in temperature down to 100 K, and its relative intensity also increased concomitantly. This result was attributed to the lower probability of the escape of the ortho-positronium (o-Ps) from the mesopores into the intergrain space at lower temperatures. An anomalous and sudden increase in the lifetime was observed at around 100 K; this result was in agreement with an increase in the positron lifetime reported in a previous study. It was revealed that the increase in the lifetime is very steep in cases of uniform mesopores, suggesting that the temperature dependence is influenced by the pore size.     

Iron oxide nanoparticles within the pore system of mesoporous SBA-15 in different acidity: the synthesis and characterization

Direct hydrothermal method is employed for incorporating iron into the pore structure of SBA-15. The resultant materials were analyzed by X-ray diffraction (XRD) patterns, N₂ sorption isotherm and X-ray photoelectron spectroscopy (XPS). The characterizations of XRD patterns and XPS revealed that iron nanoparticles were present as highly dispersed nanoclusters in the well-ordered mesoporous channels of SBA-15. The characterizations of t-plot reveal only microporous channels of SBA-15 are confirmed to be filled with iron nanoparticles, leaving the mesopores unaffected. The supported material still maintained its ordered mesoporous structure similar to SBA-15 and possessed high surface area, large pore volume and uniform pore size.     

Facile assembly of mesoporous silica nanoparticles with hierarchical pore structure for CO2 capture

A facile one-pot hydrothermal approach has been developed for the preparation of mesoporous silica nanoparticles (MSNs) with hierarchical pore structure. The PEI-modified MSNs exhibit an improved adsorption capacity for CO₂ capture.     

Facile assembly of mesoporous silica nanoparticles with hierarchical pore structure for CO2 capture

In the work, we propose an efficient one-pot approach for synthesis of a new type of mesoporous silica nanoparticles (MSNs). That can be successfully realized by using tetraethylorthosilicate (TEOS) and N-[3-(trimethoxysilyl)propyl]ethylenediamine (TSD) as the silica precursors and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent through a facile assembly process. The as-synthesized MSNs possess a spherical morphology with about 230 nm, a relatively high surface area of 133 m²/g, and a hierarchical pore size distribution. When applied as the sorbents, the amine-functioned MSNs demonstrate the enhanced adsorption capacity for CO₂ capture (at 1 bar, 15 vol% CO₂, up to 80.5 mg/g at 75 °C), high selectivity, and good cycling durability, benefiting from the suitable modification of polyethyleneimine.     

Facile synthesis of blue-emitting carbon dots@mesoporous silica composite spheres

This paper reported a facile and effective approach towards high-efficient composite luminophores by embedding blue-emitting N-doped carbon dots into spherical SiO₂ matrix (CDs@SiO₂). Mesoporous silica microspheres (r-CDs@MSN) with strong luminescence were synthesized by removing CTAB templates in CDs@SiO₂ using reflux with acetone. The r-CDs@MSN possess a spherical morphology with smooth surface and a diameter of 130 nm, while it exhibits an excitation-independent blue emission peak at 440 nm with an internal quantum yield of 21.5%. BET result shows that the corresponding surface area and adsorption total pore volume are 156.27 m²/g and 0.682 cm³/g, which is suitable for the drugs loading and release. The results indicate that r-CDs@MSN might act as a potential fluorescent drug carrier.     

Effect of synthesis conditions on the mesoscopical order of mesoporous silica SBA-15 functionalized by amino groups

Mesoporous amine-functionalized SBA-15 silica has been synthesized directly by the co-condensation of tetraethyl orthosilicate (TEOS) and aminopropyl-trimethoxysilane (APTMS) under acidic conditions with an APTMS/(APTMS + TEOS) molar ratio of 10%. The effect of synthesis conditions, including TEOS pre-hydrolysis, as well as the heating temperature and time, on the mesoscopical order and pore structure of the functionalized SBA-15 have been studied in detail by means of powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, infrared spectra and solid state ²⁹Si nuclear magnetic resonance. A functionalized SBA-15 silica with a highly ordered two-dimensional P6 mm hexagonal symmetry and a narrow pore size distribution centered at 6 nm can be obtained if TEOS is allowed to pre-hydrolyze for 2 h. For the sample with TEOS pre-hydrolysis time of 4 h, aging at 50°C or 150°C leads to a more ordered pore arrangement compared to 100°C and also a narrower pore size distribution with larger pore volume. Increasing aging time is in favor of the formation of mesoscopically ordered structure, but fails to obtain a superior pore structure.     

A chiral Mn(III) salen complex immobilized onto ionic liquid modified mesoporous silica for oxidative kinetic resolution of secondary alcohols

A supported ionic liquid strategy has been applied for the immobilization of a chiral Mn(III) salen complex onto ionic liquid modified mesoporous silica SBA-15. The immobilized catalyst demonstrated high enantioselectivity and activity in the oxidative kinetic resolution of secondary alcohols, and could be recycled five times without obvious loss of activity.     

Synthesis of large-pore SBA-15 silica using poly(ethylene oxide)-poly(methyl acrylate) diblock copolymers

Poly(ethylene oxide)-poly(methyl acrylate) diblock copolymers with narrow molecular weight distributions were synthesized using atom transfer radical polymerization. The copolymers were used as micellar templates for the synthesis of mesoporous silicas. The products were characterized using small-angle X-ray scattering, transmission electron microscopy (TEM) and nitrogen adsorption. The obtained silicas exhibited two-dimensional hexagonal structures of cylindrical mesopores, and thus can be classified as SBA-15 silicas. In some cases, the size of ordered domains was very small. The (100) interplanar spacings were 13–17 nm, depending on the size of the diblock copolymer used and on the synthesis conditions. Nitrogen adsorption showed that the silicas exhibited specific surface areas of 350–800 m² g⁻¹, pore volumes ∼1 cm³ g⁻¹, and narrow pore size distributions. The BJH (nominal) pore diameters were up to ∼20 nm, but actual diameters of cylindrical pores are expected to be somewhat smaller. In many cases, the mesopores exhibited constrictions.     

分子筛孔结构和酸性对二甲苯异构化反应性能影响

我们成功合成了几种具有典型结构的分子筛,并考察了这些分子筛的孔结构、酸性以及在碳八芳烃异构化反应中的反应性能.结果表明,对于碳八芳烃异构化反应,孔结构和酸性起着重要作用,孔结构决定了反应的类型或方式,而酸性质与反应的活性和选择性密切相关,一个好的碳八芳烃异构化催化剂要同时具备适宜的孔道结构和酸性.     

Facile one-pot synthesis of PEGylated monodisperse mesoporous silica nanoparticles with controllable particle sizes

In this work, we describe the one-pot synthesis of PEGylated mesoporous silica nanoparticles （MSNs） with uniform shape, tunable sizes, and narrow size distributions. The size of these nanoparticles can be controlled from 49 nm to 98 nm by simply varying the concentration oftriethanolamine during the base- catalyzed sol-gel reaction. Particles were characterized by transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectrometry, thermogravimetric analysis, and nitrogen adsorption-desorption measurements. These PEGylated MSNs exhibited excellent long-term stability in biological media, which ensures their potential applications in drug delivery.     

Direct synthesis of amino-functionalized monodispersed mesoporous silica spheres and their catalytic activity for nitroaldol condensation

New amino-functionalized monodispersed mesoporous silica spheres (MMSS) were synthesized directly by co-condensation of 3-aminopropyltrimethoxysilane (AP-TMS), [3-(2-aminoethylamino)propyl]trimethoxysilane (AEAP-TMS) or 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEAEAP-TMS) with tetramethoxysilane. By changing the methanol ratio or adding extra silica source, amino-functionalized MMSS with different particle diameter (310–780 nm) and the same mesopore size were successfully synthesized. TEM observations revealed that the mesopores were aligned radially from the center towards the outside of the spheres even in the amino-functionalized MMSS. The effect of particle diameter on base catalytic activity was investigated using the amino-functionalized MMSS. In addition, the amino-functionalized MMSS were found to be excellent base catalysts in the nitroaldol condensation reactions. The effectiveness factor was evaluated to be 0.8–0.82 and improved substantially compared with MMSS prepared by grafting method.     

A mesoporous silica/fluorinated alcohol adduct: an efficient metal-free,three-component synthesis of indazolophthalazinetrione heterocycles using a reusable nanoporous/trifluoroethanol adduct (SBA-15/TFE)

The channels of mesoporous (SBA-15) represent a straightforward reactor for the rapid synthesis of indazolophthalazinetrione skeletons via three-component coupling reactions in 2,2,2-trifluoroethanol. The solid SBA-15 and TFE could be recovered and reused. The present method carries the advantage of being performed under neutral conditions and requires no activation or modification of the substrates.     

Laser desorption/ionization mass spectrometric analysis of small molecules using fullerene‐derivatized silica as energy‐absorbing material

In spite of the growing acceptance of matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry for the analysis of a wide variety of compounds, including polymers and proteins, its use in analyzing low‐molecular‐weight molecules (<1000m/z) is still limited. This is mainly due to the interference of matrix molecules in the low‐mass range. Here the derivatized fullerenes covalently bound to silica particles with different pore sizes are applied as thin layer for laser desorption/ionization (LDI) mass spectrometric analysis. Thus, an interference of intrinsic matrix ions can be eliminated or minimized in comparison with the state‐of‐the‐art weak organic acid matrices. The desorption/ionization ability of the developed fullerene–silica materials depends on the applied laser power, sample preparation and pore size of the silica particles. Thus, fullerene–silica serves as an LDI support for mass spectrometric analysis of molecules (<1500 Da). The performance of the fullerene–silica is demonstrated by the mass analysis of variety of small molecules such as carbohydrates, amino acids, peptides, phospholipids and drugs. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of the order of Ni and Ce addition in SBA-15 on the activity in dry reforming of methane

Dry reforming of methane has been carried out on SBA-15 catalysts containing 5 wt% Ni and 6 wt% Ce. The effect of the order of Ni and Ce impregnation on the catalytic activity has been studied. Both metals were added using the “two-solvent” method that favors metal dispersion inside the pores. Characterizations by XRD (low and high angles), N₂ sorption, SEM and TEM of the materials after metal addition and calcination indicate good preservation of the porosities and high NiO and CeO₂ dispersion inside the porous channels. Reduction was carried out before the catalytic tests and followed by TPR measurements. The most active reduced catalyst was the Ni–Ce/SBA-15 sample prepared by impregnating cerium first, then nickel. All catalysts were highly active and selective towards H₂ and CO at atmospheric pressure. Full CH₄ conversion was obtained below 650 °C. The higher performances compared to those reported in the literature for mesoporous silica with supported Ni and Ce catalysts are discussed.     

Microwave-induced selective synthesis of α-bromo and α,α-dibromoalkanones using dioxane-dibromide and silica gel under solvent-free conditions

Selective synthesis of α-bromo and α,α-dibromoalkanones using dioxane-dibromide and silica gel in solvent-free conditions under microwave irradiation has been reported. The amount of dioxane-dibromide, silica gel and time of irradiation are keys for the selective synthesis of α-bromo and α,α-dibromoalkanones.     

Functionalized CoFe2O4/lamellar mesopore silica anchored to melamine nanocomposite as a novel catalyst for synthesis of 4H-chromenes under mild conditions

In this research, it was displayed an efficient method for the one-pot reaction of cyclohexanone, benzaldehyde and malononitrile for the synthesis of 4H-chromenes by using CoFe₂O₄/lamellar mesopore silica anchored to melamine as a magnetic nanocatalyst. This nanocatalyst was prepared in several steps and discriminated by XRD, FT-IR, SEM, VSM, TGA and BET techniques. The catalyst has a large active base site that has functionalized in both the surface and the pore of nanostructure. The advantages of magnetic nanocatalyst were simple accessible, heterogeneous nanocatalyst, easy work up and reusability. The various derivatives of 4H-chromenes were synthesized in the presence of CoFe₂O₄/lamellar mesopore silica/melamine magnetic nanocatalyst with the excellent yields and appropriate times. The products were identified by the melting point, FT-IR, ¹H NMR, ¹³C NMR and C.H.N techniques.     

Copper/Schiff-base complex immobilized on amine functionalized silica mesoporous magnetic nanoparticles under solvent-free condition: A facile and new avenue for the synthesis of thiazolidin-4-ones

A copper/Schiff-base complex supported on amine-functionalized silica mesoporous magnetic nanoparticles was prepared as novel magnetically interphase nanoparticles and its morphology and structure were evaluated using Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, zeta potential, and a vibrating sample magnetometer. The catalytic activity of the synthesized nanoparticles was evaluated for the synthesis of thiazolidine-4-ones.